65
Adjustments
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result
in excess overfire and heat exchanger failures.
!
WARNING
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT redrill orifices. Improper drilling (burrs,
out
−
of
−
round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. This can result in flame
impingement of heat exchangers, causing failures. See Fig.
CAUTION
!
For proper operation and long term reliability, the Furnace input
rate must be /
−
2 percent of input rate on furnace rating
plate, or as adjusted for altitude.
The gas input rate on rating plate is for installations at altitudes up
to 2000 ft. (609.6M).
The NATURAL GAS manifold pressure adjustments in Table
22 compensate for BOTH altitude AND gas heating value.
DO NOT apply an additional de
−
rate factor to the pressures
show in Table 22. The values in this table are NOT referenced
to sea level; they are AS
−
MEASURED AT ALTITUDE.
The heating content of natural gas at altitude may already
provide for a reduction in capacity of the furnace. Be sure to
obtain the expected in
−
season gas heating value of the gas
from the gas supplier BEFORE making any adjustments for
capacity or altitude. Refer to Table 22. No adjustments to the
furnace may be necessary at altitude for certain gas heating
values.
Refer to the instructions provided in the factory
−
specified
LP/Propane conversion kit for instructions for setting gas
manifold pressures for LP/Propane applications.
NOTICE
In the USA, the input rating for altitudes above 2000 ft. (609.6M)
must be reduced by 2 percent for each 1000 ft. (304.8M) above sea
level. Refer to Table 20. The natural gas manifold pressures in
Table 22 adjust for BOTH altitude and natural gas heating value.
In Canada, the input rating must be reduced by 5 percent for
altitudes of 2000 ft. (609.6M) to 4500 ft. (1371.6M) above sea
level. The natural gas manifold pressures in Table 22 adjust for
BOTH altitude and natural gas heating value.
NOTE
: For Canadian altitudes of 2000 to 4500 ft. (610 to 1372
M), use USA altitudes of 2001 to 3000 ft. (611 to 914 M) in Table
22.
To adjust manifold pressure to obtain the proper input rate, first,
determine if the furnace has the correct orifice installed. At higher
altitudes or different gas heat contents, it may be necessary to
change the factory orifice to a different orifice. Tables have been
provided in the furnace installation instructions to match the
required orifice to the manifold pressure to the heat content and
specific gravity of the gas. To do this:
1. Obtain average yearly gas heat value (at installed altitude)
from local gas supplier.
2. Obtain average yearly gas specific gravity from local gas
supplier.
3. Find installation altitude in Table 22.
4. Find closest natural gas heat value and specific gravity in
Table 22. Follow heat value and specific gravity lines to
point of intersection to find orifice size and manifold
pressure settings for proper operation.
5. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
If orifice hole appears damaged or it is suspected to have been
redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr
−
free and squarely
aligned orifice hole is essential for proper flame characteristics.
NOTICE
6. Replace orifice with correct size, if required as shown in
Table 22. Use only factory
−
supplied orifices. See
EXAMPLE 1.
EXAMPLE
1: 0
−
2000 ft. (0
−
609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
(Furnace is shipped with No. 44 orifices. In this example, all main
burner orifices are the correct size and do not need to be changed to
obtain proper input rate.)
Manifold pressure: 3.4
−
in. W.C. (847 Pa).
NOTE
: To convert gas manifold Table pressures to Pascals,
multiply the in. W.C. value by 249.1 Pa/in. W.C. (1 in. W.C. =
249.1 Pa).
Check Inlet Gas Pressure
The inlet gas pressure must be checked with the furnace operating
in maximum heat. This is necessary to make sure the inlet gas
pressure does not fall below the minimum pressure of 4.5 in. w.c.
1. Make sure the gas supply is turned off to the furnace and at
the electric switch on the gas valve.
2. Loosen set screw on inlet tower pressure tap no more than
one full turn with a 3/32
−
in. hex wrench or remove the
1/8
−
in. NPT plug from the inlet pressure tap on the gas
valve.
3. Connect a manometer to the inlet pressure tap on gas valve.
4. Turn on furnace power supply.
5. Turn gas supply manual shutoff valve to ON position.
6. Turn furnace gas valve switch to ON position.
7. Jumper R and W thermostat connections at the furnace
control board.
8. When main burners ignite, confirm inlet gas pressure is
between 4.5 in. w.c. (1125 Pa) and 13.6 in. w.c. (3388 Pa).
9. Remove jumper across thermostat connections to terminate
call for heat. Wait until the blower off delay is completed.
10. Turn furnace gas valve electric switch to OFF position.
11. Turn gas supply manual shutoff valve to OFF position.
12. Turn off furnace power supply.
PG92S*S
